Controlled hydrocracking process



Feb. 27, 1962 F. G. CIAPETTA ErAL 3,023,159

CONTROLLED HYDROCRACKING PROCESS 2 Sheets-Sheet 2 Filed March 9, 1956 mI o I 8 L w fi W S 0m 4V 7/ M c m m m m m m 0 INVENTORS United StatesPatent 3,023,159 CDNTROLLED HYDRUCRAQQNG PROCESS Frank G. Ciapetta,Upper Darby, Pm, and Harry L.

Coonradt, Woodbury, and William E. Garwood, Haddonfield, N.J., assignorsto Socony, Mobil Gil Company, Inc., a corporation of New York Filed Mar.9, 1955, Ser. No. 570,440 3 Claims. (Cl. 208l) Number 418,166, filedMarch 23, 1954, a continuation- I in-part thereof, now abandoned, and incopending application Serial Number 825,016, filed July 6, 1959, now US.Patent No. 2,945,806, issued July 19, i960, a continuation-in-partthereof, there is disclosed a process for cracking hydrocarbons in thepresence of catalysts comprising metals of the platinum and palladiumseries depositedupon refractory acidic oxides. It is a preferred featureof that process that the nitrogen content of the charge must'be belowabout 0.1'percent, by weight, and preferably lower than about 0.08percent, by Weight. Under such conditions, by correlation of thetemperature and of the liquid hourly space velocity the process could beoperated to produce gasoline and/or fuel oil in any ratio varying fromsubstantially 100 percent yield of gasoline to substantially 100 percentyield of fuel oil. In such an operation the cetane index of the fuel oilproduced is relatively high and varies dependent upon the degree ofconversion in the process.

As is well known to those skilled in the art, however, it is desirablein practical refinery operation to maintain the cetane index of the fueloil substantially constant regardless of the ratio between the amount offuel oil produced and the amount of gasoline that may be produced. Thus,depending upon seasonal demands, it will be necessary to produce greateror lesser amounts of gasoline; yet, at the same time it is desirable tomaintain the quality of'the fuel oil substantially constant. As is alsowell known to those familiar with the art, greater amounts of hydrogenare consumed in a cracking process to produce fuel oilshaving relativelyhigh cetane indices. Practically speaking, however, relatively highcetane index fuel oil is not always desired, in order to maintain acompetitive quality fuel oil. In such cases, it will be readilyappr'eciatedthat great savings in operational cost can be effected ifthe cracking process can be operated under conditions to provide a fueloil in any yield that has a relatively lower cetane index, butsubstantially uniform quality.

It has now been'found that a process for the cracking of heavyhydrocarbons in contact with hydrogen and with catalysts containingmetals of the platinum and palladium series can be operated underconditions whereby there is effected the production of fuel oils havingsubstantially the same cetane index regardless of the yield, which fueloils haverelatively lower cetane index; It has been discovered that sucha processrcan be controlled by operating at substantially constanttemperature and by controlling the arnount of conversion in the processby regulating the nitrogen content of the hydrocarbon charge stock.

Accordingly, it is an object of this inventionto provide an improvedprocess for cracking in the presence of hydrogen and of catalystcomprising platinum or palladium' series metals supported uponrefractory acidic oxide 2 carriers. Another object is to provide aprocess for controlling the cetane index in the fuel oils obtained inthe cracking process. A further object is to provide a method forregulating the amount of hydrogen consumed in a cracking process carriedout in the presence of hydrogen. A further object is to provide a methodfor producing fuel oils having substantially uniform quaiity regardlessof the yield thereof. A specific object is to provide a method formaintaining the uniformity and quality of fuel oil produced by crackinga relatively high boiling hydrocarbon fraction in the presence ofplatinum and palladium series metal containing catalysts that involvesoperating the process at substantially uniform temperature andcontrolling the amount of conversion in the process by regulating thenitrogen content of the charge.

Other objects and advantages of the present invention can becomeapparent to those skilled in the art from the following detaileddescription considered in conjunction with the drawings, wherein:

FIGURE 1 presents the graphic relationship between the volume percentconversion into products boiling at temperatures lower than about 390 F.and the temperature obtained by cracking a typical gas oil in thepresence of hydrogen and of aplatinum-containing catalyst;

FIG. 2 presents the graphic relationship between the yield of fuel oiland the cetane index thereof, obtained by cracking a typical gas oil inthe presence of hydrogen and of a platinum-containing catalyst, bothwith and without the addition of a nitrogenous compound to the feed;

FIG. 3 presents the graphicrelationship between the volume percentconversion into products boiling at ternperatures lower than about 390F. and the weight percent nitrogen in the charge stock obtained bycracking a typical gas oil in the presence of hydrogen and of aplatinum-containing catalyst with varying amounts of nitrogen in thecharge; and

FIG. 4 presents the graphic relationship betweenthe volume percentconversion into products boiling at temperatures lower than about 390 F.and the hydrogen consumption when a typical gas oil is cracked in thepresence of hydrogen and of a platinum-containing catalyst in a processwherein no nitrogen is added to the feed, and also in a process whereinvarying amounts of nitrogen are added to the feed. V

In general, the present invention provides, in a process for convertinga hydrocarbon fraction having an initial boiling point of at least about400 F., a 50 percent point of at least about 500 F. and an end boilingpoint of at least about 600 F. and boiling substantially continuouslybetween said initial boiling point and said end boiling polnt intogasoline and/or fuel oil that comprises contasting said hydrocarbonfraction with a catalyst comprising between about 0.05 percent and about20 percent by weight of the catalyst of at least one metal of theplatinum and palladium series deposited upon a synthetic composite ofoxides of at least two metals of groups IIA, IIIB and IV of the periodicarrangement of elements having an activity index of at least 25 in'theLpresence'of 1 hydrogen inamountsexpressed in molar ratio of hydrogentohydrocarbon chargevarying between about 2 and about 80, at pressuresvarying betwe'enabout psig and about 2500 p.s.i.g., at a liquid hourlyspace velocity varying between about 0.1 and about 10, and attemperatures varying between about 600 F. and about 900 F., the methodof operation'that comprises operating said process at substantiallyconstant temperature and controlling-"the amount of conversionintofproducts boilingv at temperatures lower than about 390 F. byregulating the nitrogen content of said hydrocarbon fraction within therange varying between about 0.01 percent, by weight, and about 1.0percent, by weight;

Throughout the specification and the claims, the term Patented Feb, 27,1962 conversion is intended to be a generic term for the amount ofproducts boiling at temperatures lower than about 390 F. (l-recycle), ofgasoline, or of fuel oil obtained in the process. It is expressed interms of the volume percent of the initial charge which is transformedin the process. The amount of product boiling at temperatures lower thanabout 390 F. is obtained by subtracting the volume percent of cyclestock (fuel oil) from 100 percent, i.e., from the initial volume of thecharge. The expression IOU-recycle) is an abbreviation for 100 percentminus the volume percent recycle. As the cycle stock (i.e., the effiuentboiling at temperatures higher than about 390 F.) is an excellent fueloil, conversion into fuel oil is the volume percent of product whichboils at temperatures higher than about 390 F. The volume percent ofconversion into products boiling at temperatures lower than about 390 F.(100-recycle) and the volume percent of conversion into fuel oil totalsto 100 volume percent, based upon the initial charge. Dry gas refers tothe methane, ethane, propane, and ethylene and propylene produced in acracking process, expressed in terms of weight percent of the initialcharge. Light naphtha is the product that boils between about 125 F. andabout 170 F. The heavy naphtha is the product that boils between about170 and about 390 F. The cetane index is a measure of ignition qualityof a fuel, as described in ASTM test D975-53T, appendix II. The crackingactivity of a carrier is expressed in terms of the percent, by volume,of a standard hydrocarbon charge which is cracked, under specificoperating conditions, in the Cat. A test. This test is described byAlexander and Shimp in National Petroleum News, 36, page R-537 (August2, 1944). The unit for rating the cracking activity of a material iscalled the activity index (Al).

The catalysts utilizable herein are those described in copendingapplication Serial Number 351,151, filed on April 27, 1953, nowabandoned; and in the continuationin-part thereof Serial Number 418,166,filed on March 23, 1954-, now abandoned; and in continuation-in-partthereof, Patent No. 2,945,806, filed on July 6, 1959. Briefly, thesecatalysts comprise between about 0.05 percent, by Weight, and about 20percent, by weight of the final catalyst, preferably between about 0.1percent and about 5 percent, by weight, of the metals of the platinumand palladium series, i.e., those having atomic numbers of 44-46,inclusive, 76-78, inclusive, supported upon synthetic composites of twoor more refractory oxides. The carrier is a synthetic composite of twoor more oxides of the metals of groups HA, IIIB and IVA and B of theperiodic arrangement of elements [1. Chem. Ed., 16, 409 (1939)]. Thesesynthetic composites of refractory oxides must have an activity index ofat least about 25. They can also contain halogens and other materialswhich are known in the art as promoters for cracking catalysts, or smallamounts of alkali metals that are added for the purpose of controllingthe activity index of the carrier. Non-limiting examples of thecomposites contemplated herein include silica-alumina, silica-zirconia,silica-alumina-zirconia, alumina-boria, silica-alumina-fluorine, and thelike. The preferred support is a synthetic composite of silica andalumina containing between about 1 percent, by weight, and about 90percent, by weight, of alumina. These synthetic composites of two ormore refractory oxides can be made by any of the usual methods known tothose skilled in the art of catalyst manufacture. Examples of methods ofpreparing them are set forth in abandoned applications Serial Nos.351,151 and 418,166 and Patent No. 2,945,806.

The following example illustrates a method of preparing aplatinum-containing catalyst utilizable in the process of thisinvention:-

EXAMPLE 1 A synthetic silica-alumina carrier or support containing 10percent by weight alumina was prepared by mixing an aqueous solution ofsodium silicate (containing 158 g. per liter of silica) with an equalamount of an aqueous acid solution of aluminum sulfate containing 39.4g. A1 (S0 and 28.6 g. concentrated H 80 per liter. This mixture ofsolutions was dropped through a column of oil, wherein gelation of thehydrogel was effected in head form. The head hydrogel was soaked in hotwater (about 120 F.) for about 3 hours. The sodium in the hydrogel wasthen removed by exchanging the gel with an aqueous solution of aluminumsulfate [1.5% Al (SO.,) by weight] containing a small amount (0.2percent by weight) of ammonium sulfate. The thus-exchanged hydrogel headwas water-washed. Then, it was dried in superheated steam (about 280-340F.) for about 3 hours and, finally,

calcined at 1300 F. under a low partial pressure of steam for about 10hours. 1

The silica-alumina beads were then crushed to pass through a l4-meshscreen and the material retained on a ZS-mesh screen (US. StandardScreen Series) was used for catalyst preparation. Portions of thecrushed, calcined carrier were then barely covered with aqueoussolutions of chloroplatinic acid, of concentrations suflicient toproduce the desired amount of metal in the finished catalyst. The excesssolution was removed by centrifuging. The thus-impregnated carrier wasthen aged in a lightly covered vessel at 230 F. for 24 hours. Thecatalyst was treated with hydrogen for 2 hours at 450 P. Then, it wasactivated in hydrogen for 2 hours at 900 F. before it was used. Thecatalyst thus prepared contained 0.47 percent platinum, by weight of thecatalyst, and the silica-alumina carrier had an activity index of 46.

The charge stocks ntilizable herein are hydrocarbon fractions having aninitial boiling point of at least about 400 F., a 50 percent-point of atleast about 500 F. and an end-boiling point of at least about 600 F. andboiling substantially continuously between said initial boiling pointand said end-boiling point. Such charge stocks include gas oils,residual stocks, refractory cycle stocks from conventional cracking,whole topped crudes, and heavy hydrocarbon fractions derived by thedestructive hydrogenation of coal, tars, pitches, asphalts, etc., suchas, for example, middle 0' As is well known to thOSe skilled in the art,the distillation of higher-boiling petroleum fractions (those boiling attemperatures higher than about 750 F.) must be carried out under vacuum,in order to avoid thermal cracking. Throughout the specification and inthe claims, however, the boiling temperatures are expressed in terms ofthe boiling point at atmospheric pressure. In other words, in allinstances, the boiling points of fractions distilled under vacuum havebeen corrected to the boiling points at atmospheric pressure.

As is well known to those familiar with the art, the term gas oil is abroad, general term that covers a variety of stocks. Throughout thespecification and in the claims, the term, unless further modified,includes any fraction distilled from petroleum which has an initialboiling point of at least about 400 F., a 50 percent-point of at leastabout 500 R, and an end-boiling point of at least about 600 F., andboiling substantially continuously between the initial boiling point andthe end-boiling point.

The portion which is not distilled is considered residual stock. Theexact boiling range of a gas oil, therefore, will be determined by theinitial distillation temperature (initial boiling point) the 50percent-point, and by the temperature at which distillation is cut oif(end-boiling point).

In practice, petroleum distillations have been made under vacuum up totemperatures as high as 11004200 F. (corrected to atmospheric pressure).Accordingly, in the broad sense, a gas oil is a petroleum fraction whichboils substantially continuously between two temperatures that establisha range falling within from about 400 F. to about 1100-1200" F., the 50percent-point being at least about 500 F. Thus, a gas oil could boilover the entire range 400-1200 F. or it could boil over a narrowerrange, e.g., 500-900" F.

The gas oils can be further roughly subdivided by overlapping boilingranges. Thus, a light gas oil boils between about 400 F. and about600-650 F. A medium gas oil distills between about 600-650" F. and about700-750 F. A heavy gas oil will boil between about 600-650 F. and about800-900" F. A gas oil boiling between about 800-850" F. and about1100-1200 F. is sometimes designated as a vacuum gas oil. It must beunderstood, however, that a gas oil can overlap the foregoing ranges. Itcan even span several ranges, i.e., include, for example, light andmedium gas oils.

As mentioned hereinbefore, a residual stock is any fraction which is notdistilled. Therefore, any fraction, regardless of its initial boilingpoint, which includes all the heavy bottoms, such as tars, asphalts,etc., is a residual fraction. Accordingly, a residual stock can be theportion of the crude remaining undistilled at llO0-l200 F., or it can bemade up of a gas oil fraction plus the portion undistillecl at 1100-1200F. A whole topped crude, as the name implies, is the entire portion ofthe crude remaining after the light ends (the portion boiling up toabout 400 F.) have been removed by distillation. Therefore, such afraction includes the entire gas oil fraction (400 F. to 1100-1200" F.)and the undistilled portion of the crude petroleum boiling abovel100-l200 F. If it is desired, the residual fractions and thewholetopped crude can be deasphalted by anymeans known to the art. Suchtreatment, however, is not necessary for charge stocks intended for usein the process of this invention.

The refractory cycle stocks are cuts of conventionmly cracked stockswhich boil above the gasoline boiling range, usually, between about 400F. and about 850 F. The refractory cycle stocks can be charged to theprocess of this invention in conjunction with a fresh petroleum chargestock, or they can be charged alone to the process. The process of thisinvention is particularly adaptable to the cracking of sulfur-containingcharge stocks. The catalysts utilizable in the process of thisinvention, quite unexpectedly, are not deactivated by sulfur compounds,under the conditions of the process.

The hydrogen pressure used varies between about 100 pounds per squareinch gauge and about 2500 pounds per square inch gauge, preferably,however, between about 350 and about 2000 pounds per square inch gauge.The liquid hourly space velocity, i.e., the liquid volume of hydrocarbonper hour per volume of catalyst varies be- EXAMPLE 2 The-charge stockused in this example was obtained by coking a Mid-Continent residualfraction. This coker gas oil had the following properties:

ARE. gravity 33.3

ASTM distillation:

I.B.P -F 420 50% F 535 F 664 Sulfur, weight percent 0.48 Nitrogen,weight percent 0.08 Cetane index 47.7

Portions of this coker gas oil were'cracked in the presence I ofhydrogen and of the platinum catalyst described in Example 1 after thelatter had reached equilibrium, ife., had been in continuous operationfor more than 5 days. Each run was carried out at a differenttemperature, using a hydrogen-to-oil molar ratio of 40; a'pressure ofabout 1000 p.s.i.g. and a liquid hourly space velocityof 0.5. Thepertinent results of these runs lareset'iforth in Table I.

Table 1 39g flonversion into products boiling .at temperatures lowerthan about The curve in FIG. 1 is basedupon'the data set forth in aTable I. This curve shows the relationship between the volume percentconversion into products boiling at temperatures lower than about-390 E.and the. temperature, when a typical gas oil is cracked in the presenceof the platinum-containing catalyst It. willbe noted that. the amount ofconversion is.a-direct functionof the temperature, other variablesbeingconstant. -.This,..of course, represents one method of controllingthe. outputof the cracking process. The curvein FIG; 1, however, must becousideredin conjunction .with curve A in FIG. 2. The latter curve, alsobased upon data set forth in Table I, shows the relationship between thevolume percent conversion into fuel oil and the cetane index of the fueloil. It is to be noted that as the yield of fuel oil varies, the cetaneindex varies. Such operation does not permit the maintenance of uniformfuel oil quality togetherwith nitrogen content of the charge tocontrol-theamount of conversion. w e arm est t e} th follvwing.

examples.

AMPLE The charge "stock used in thisexample was a gas' oil obtainedby-co-king a-coastalresidual w-hichgas oilhad been subjected to a hydrofinishing-operation to -reduce its nitrogen-content to 0.04-weightpercent. This material had the following properties:

A.P.I gravity 32.6 ASTM distillation;

I.B.P. F 290 50% I F 520' E1. R. 64 Sulfur, weight percent 0.001Nitrogen, weight percent 0.04

This gas oil was subjected to cracking in the presenceof ydrogen. and ofthe equilib um .ca lvstfie b din Example 1.. The operation was carriedout at a pressure of 1000 p.s.i.g. using a hydrogenetoroil molar ratioof 40 and z -liquid hourly space velocity of 0.5. The

catalyst temperature was 760 E -Under these conditions there waseffected 76 volume percent conversion into products boiling attemperaturelower. than about 390 F. Pertinent results are set forth inTable II.

EXAMPLE 4 The charge stock used in this example was another portionofthe coastal poker gas oil that hadbeen. subjected to hydro-finishingoperation to reduce the nitrogen content thereof to 0.1 weight percent.This material had the following properties:

A.P.I. gravity 31.7 ASTM distillation:

I.B.P. F 276 50% F 520 E.P. F 644 Sulfur, weight percent 0.02 Nitrogen,weight percent 0.10

This gas oil was subjected to cracking in the presence of hydrogen andhad the same catalyst used in Example 3. The operation was carried outunder the same conditions used in Example 3. Under these conditions,there was effected 51 volume percent conversion into products boiling attemperatures lower than about 390 F. Pertinent I data are set forth inTable II.

EXAMPLE The charge stock used in this run is another portion of thecoastal coker gas oil that had been subjected to hydro-finishingoperation to lower the nitrogen content to 0.12. This material had thefollowing properties:

A.P.I. gravity 31.5. ASTM distillation:

I.B.P. 346 F. 50% 524 F. E.P. 644 F. Sulfur, weight percent Less than0.001. Nitrogen, weight percent 0.12.

The charge stock used in this run was still another portion of thecoastal coker gas oil that had been subjected to a hydro-finishingoperation to reduce the nitrogen content thereof to 0.24 weight percent.It had the following properties:

A.P.I. gravity 30.7

ASTM distillation:

1.13.1 -F 354 50% F 528 El. F..- 642 Sulfur, weight percent 0.055Nitrogen, weight percent 0.24

This gas oil was subjected to cracking in the presence of hydrogen andof the platinum catalyst used in the run described in Example 3. The runwas operated under the same conditions set forth in Example 3. Underthese conditions there was elfected 14 volume percent conversion intoproducts boiling lower than about 390 F. Pertinent data are set forth inTable II.

Table II Example 3 4 b 6 Percent nitrogen in charge 0. 04 0. 10 0. 12 0.24 Temperature, F 760 760 760 7150 Conversion, volume percent k. 76 5137 14 Dry gas, weight percent 2. 8 1. 9 1. 9 0.7 Butanes, volume percent11. 2 8. 7 4. 7 1. 7 05+ light naphtha, volume perce 17. 9 10. 6 6. 92.0 Heavy naphtha, volume percent- 60 43 33 15 Fact 01], volume percent;24 49 63 86 Octane index of fuel oil 45 45 44 43. 5 Hydrogenconsumption, c.1.[b 1, 200 940 660 220 1 CI nversImJ into productsboiling at temperatures lower than about 390 r The curve set forth inFIG. 3 is based upon the data Table II. This curve presents the graphicrelationship between the volume percent conversion into products boilingat temperatures lower than about 390 F. and the nitrogen content of thecharge, when a hydrocarbon charge is cracked using the same catalysttemperature but varying the nitrogen content. It will he noted that asthe nitrogen content of the charge is varied between about 0 weightpercent and about 0.3 weight percent, the charge stock can be cracked atvirtually any conversion level While operating at the same temperaturethroughout. In other words, as com-pared with the data presented in FIG.1, the control of the cracking level was achieved by controlling thenitrogen content of the charge, instead of by varying the reactiontemperature.

This control of the nitrogen content generally can be effected inseveral ways or by a combination thereof. One method involves theaddition of nitrogenous compounds to the charge stock in amountssufiicient to achieve the desired total nitrogen content that willefieot the desired degree of conversion at the operating temperatureselected. In general, any nitrogen compound that is capable of beingconverted into ammonia at the reaction conditions used is applicable.Accordingly, the added compounds can be inorganic nitrogen compounds orthey can be organic nitrogen compounds, such as amines, cyclic nitrogenmaterials, hydrazines and the like. Nonlimiting examples of the nitrogencontaining compounds utilizable herein are ammonia, Z-methylpyridine,2-rnethylpiperidine, pyrrole, pyrrolidine, quinoline, acridine, andcarbazole. Another source of-added nitrogen is a gas oil, or otherhydrocarbon fraction, that has a high nitrogen content, e.g., aCalifornia thermally cracked gas oil. It will be appreciated that theregulation of nitrogen content by means of added nitrogen compounds ismore generally applicable to charge stocks that have a relatively lownitrogen content. In such a case, the amount of nitrogen compound addedwill be suflicient to bring the total nitrogen content up to the desiredlevel.

Another method of controlling the nitrogen content, more generallyapplicable in the case of charge stocks having large amounts ofnitrogen, is by means of controlled reduction of the total nitrogencontent of the charge. This reduction of nitrogen content can beeffected by any of the several means well known to those skilled in theart. A particularly eiiective method is nondestructive hydrogenation toa degree just suflicient to efiect the desired amount of nitrogenremoval without materially affecting the other properties of the chargestock. A still further method of regulating the amount of nitrogen inthe feed stock is by controlling the ammonia content of thehydrogen-containing recycle gas.

Regardless of the method used for controlling the nitrogen content, theamount of nitrogen compound ultimately in the charge stock willordinarily vary between about 0.01 weight percent and about 1.0 weightpercent, preferably between about 0.01 weight percent and about 0.5weight percent. In operating the process of this invention wherein thecracking temperature is maintained constant throughout and the amount ofcracking is controlled by means of varying the nitrogen content of thefeed, the major factor that will efiect the desired nitrogen content forany given degree of conversion, is the temperature at which cracking iscarried out. The curve in FIG. 3 represents the relationship between thenitrogen content and conversion when operating at a temperature of 760F. throughout. It will be recognized, of course, that at other operatingtemperatures a dilferent range of nitrogen content will be used. Thisrange, however, can

, be expressed by curves that generally parallel the curve conversion.The less active catalysts require higher temperatures. The catalystsalso lose activity during use be cause of the build-up of carbonaceousdeposits (coke), or prolonged use, or both. Thus, another advantage ofthe process of this invention is that the cetane index or the hydrogenconsumption, or both can be maintained essentially constant even thoughthe catalyst activity changes. This can be done by raising thetemperature. It is more feasible and preferable, however, to accomplishthe desired maintenance of uniformity by lowering the amount of nitrogenadded to the charge.

As was mentioned hereinbefore, the process for the present invention isparticularly applicable in refinery processes in which the cetane indexdoes not have to be relatively high but in which it is highly desirablethat fuel oil quality expressed in terms of cetane index should remainsubstantially constant regardless of the conversion level. That this isachieved in the present process will be apparent from curve B in FIG. 2.This curve based upon the data set forth in Table II represents therelationship between rhe volume per cent conversion into fuel oil andthe cetane index of the fuel oil. As will be apparent from curve B, thecetane index of the fuel oil remains substantially constant regardlessof the conversion level. On the other hand, when cracking is carried outby means of controlling the conversion level by means of the temperature(curve A), the cetane index varies considerably with the conversionlevel. In general, also the cetane index is relatively higher than thatexpressed by curve B. Yet, a cetane index of such magnitude may not begenerally desirable. Indeed, in cases where product uniformity is moredesirable, the operation illustrated by curve B is much more desirableon a commercial basis.

A major factor, from an economical standpoint, that efiects the choiceof a process of the present type is the amount of hydrogen consumption.This is illustrated by the curves in FIG. 4. Curve C represents thegraphic relationship between the volume percent conversion into Iproducts boiling at temperatures lower than about 390 F. and the amountof hydrogen consumed when the gas oil is cracked in the presence ofhydrogen and of the platinum catalyst and by controlling the degree ofconversion by varying the temperature. Curve D presents a similarrelationship in the case in which the gas oil charge is cracked at aconstant temperature, varying the amount of conversion by controllingthe nitrogen content of the charge, in accordance with the process ofthis invention. Particularly at conversion levels lower than about 50volume percent, considerably more hydrogen is consumed at any givenconversion level when the amount of conversion is controlled by means ofthe temperature. As indicated hereinbefore, however, in many instancesthe relatively higher cetane index achieved in such an operation is notnecessary or desirable. in such a case the amount of hydrogen consumedrepresented by curve D will be sufficient to achieve the desired cetaneindex in the fuel oil. Therefore, the amount of hydrogen consumed repre-10 eliminated and the maintenance of product uniformity is achieved. 1

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the purview andscope of the appended claims.

What is claimed is:

1. In a process for the reaction of a hydrocarbon fraction having aninitial boiling point of at least 400 F., a 50 percent point of at least500 F. and an end boiling point of at least 600 F. with hydrogen in thepresence of a catalyst which comprises between about 0.05 and 20 percentby weight of at least one metal of the platinum and palladium seriesdeposited upon a composite of solid oxides of at least two elements ofgroups IIA, IIIB and IV of the periodic arrangement of elements, saidcom posite having an activity index greater than 25, wherein there is atall times a net consumption of hydrogen by said fraction and at leastperiodically the hydrocarbon fraction is converted at a reactiontemperature within the range about 600 F. to about 900 F., to lowerboiling products, the improved method of operation which comprises:adding nitrogenous compounds to said fraction to increase its nitrogencontent and periodically adjusting the quantity of nitrogenous compoundsadded to effect at least a part of the control over the extent to whichsaid hydrocarbon fraction is converted to lower boiling products, thenitrogen content of the fraction varying from time to time but at alltimes being within'the range about 0.01 to 1 percent by weight of thefraction, and at any given time an increase in added nitrogenouscompounds being used to decrease the extent of conversion of thefraction to lower boiling products and a decrease in added nitrogenouscompounds being used to increase the extent of conversion of thefraction to lower boiling products, whereby the hydrogen consumed duringconversion to lower boiling products is lower than when the same controlover the extent of conversion is effected by variation of reactiontemperature alone.

2. The process of claim 1 further limited to maintaining the reactiontemperature substantially constant within the range 600 to 900 F. andcontrolling the extent of conversion solely by regulating the nitrogencontent of the hydrocarbon fractions undergoing conversion.

3. lhe process of claim 1 further limited to continuously separating ahydrogen-containing recycle gas from the products of the reaction andreturning said recycle gas to the reaction zone and efiecting theadjustment in nitrogen content of the hydrocarbon fraction by adjustingthe ammonia content of the recycle gas.

References Cited in the file of this patent UNITED STATES PATENTS2,550,531 Ciapetta Apr. 24, 1951 2,708,180 Fuener ct a1 May 10, 19552,717,230 Murray et a1 Sept. 5, 1955 2,758,064 Haensel Aug. 7, 19562,763,623 Haensel Sept. 18, 1956 2,799,626 Johnson et al July 16, 19572,849,377 Ogburn et al Aug. 26, 1958 2,911,356 Hanson Nov. 3, 1959

1. IN A PROCESS FOR THE REACTION OF A HYDROCARBON FRACTION HAVING ANINITIAL BOILING POINT OF AT LEAST 400*F., A 50 PERCENT POINT OF AT LEAST500*F. AND AN END BOILING POINT OF AT LEAST 600*F. WITH HYDROGEN IN THEPRESENCE OF A CATALYST WHICH COMPRISES BETWEEN ABOUT 0.05 AND 20 PERCENTBY WEIGHT OF AT LEAST ONE METAL OF THE PLATINUM AND PALLADIUM SERIESDEPOSITED UPON A COMPOSITE OF SOLID OXIDES OF AT LEAST TWO ELEMENTS OFGROUPS IIA, IIIB AND IV OF THE PERIODIC ARRANGEMENT OF ELEMENTS, SAIDCOMPOSITE HAVING AN ACTIVITY INDEX GREATER THAN 25, WHEREIN THERE IS ATALL TIMES A NET CONSUMPTION OF HYDROGEN BY SAID FRACTION AND AT LEASTPERIODICALLY THE HYDROCARBON FRACTION IS CONVERTED AT A REACTIONTEMPERATURE WITHIN THE RANGE ABOUT 600*F. TO ABOUT 900*F., TO LOWERBOILING PRODUCTS, THE IMPROVED METHOD OF OPERATION WHICH COMPRISES:ADDING NITROGENOUS COMPOUNDS TO SAID FRACTION TO INCREASE ITS NITROGENCONTENT AND PERIODICALLY ADJUSTING THE QUANTITY OF NITROGENOUS COMPOUNDSADDED TO EFFECT AT LEAST A PART OF THE CONTROL OVER THE EXTENT TO WHICHSAID HYDROCARBON FRACTION IS CONVERTED TO LOWER BOILING PRODUCTS, THENITROGEN CONTENT OF THE FRACTION VARYING FROM TIME TO TIME BUT AT ALLTIMES BEING WITHIN THE RANGE ABOUT 0.01 TO 1 PERCENT BY WEIGHT OF THEFRACTION, AND AT ANY GIVEN TIME AN INCREASE IN ADDED NITROGENOUSCOMPOUNDS BEING USED TO DECREASE THE EXTENT OF CONVERSION OF THEFRACTION TO LOWER BOILING PRODUCTS AND A DECREASE IN ADDED NITROGENOUSCOMPOUNDS BEING USED TO INCREASE THE EXTENT OF CONVERSION OF THEFRACTION TO LOWER BOILING PRODUCTS, WHEREBY THE HYDROGEN CONSUMED DURINGCONVERSION TO LOWER BOILING PRODUCTS IS LOWER THAN WHEN THE SAME CONTROLOVER THE EXTENT OF CONVERSION IS EFFECTED BY VARIATION OF REACTIONTEMPERATURE ALONE.